The purpose of this project is to conduct statistical research and provide consultation to the Division for clinical trials, laboratory experiments, and epidemiological studies relevant to cancer prevention and control. Research problems under investigation include statistical models for monitoring prevention trials, evaluation of alternative measurement error models in nutritional epidemiology, statistical methods of validating intermediate or surrogate endpoints, analysis of animal experiments relating dietary fat intake to mammary tumor incidence, use of Bayesian methods for monitoring Phase II chemoprevention trials, studies on a large observational database of HIV-infected subjects with evaluation of natural history of disease, evaluation of genetic-environmental interactions in cancer, and the analysis of crossover trials. Statistical consultation is provided to numerous studies including the NIH Women's Health Initiative Clinical Trial. The consultation has involved extensive contributions to study design, study analysis, and data monitoring. A large database on Division-supported Human Intervention Studies (HINTS) has been developed. The content and format of the data collection instrument has been tested and full data collection has now begun.